1. Field of the Invention
The present invention relates to a compressor and, more particularly, to an apparatus for controlling an operation of a reciprocating compressor and its method.
2. Description of the Prior Art
In general, a reciprocating compressor (hereinafter, for simplicity, referred to as “reciprocating motor compressor”), which is operated by a linearly reciprocating electric motor without a crank shaft for converting a rotational motion to a linear motion, has less friction loss, and thus, can provide a higher compression efficiency than other compressors.
When the reciprocating motor compressor is used for a refrigerator or an air-conditioner, a compression ratio of the compressor can be varied to control the cooling capacity by varying a stroke voltage applied to the reciprocating motor of the compressor.
The conventional controlling of a reciprocating motor compressor will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing the construction of an apparatus for controlling an operation of a reciprocating compressor in accordance with a conventional art.
As shown in FIG. 1, the conventional apparatus for controlling an operation of the reciprocating compressor includes a current detector 4 for detecting a current applied to a motor (not shown) of a reciprocating compressor 6; a voltage detector 3 for detecting a voltage applied to the motor, a stroke calculator 5 for calculating a stroke estimate value of the reciprocating compressor based on the detected current and voltage values and a parameter of the motor, a comparator 1 for comparing the calculated stroke estimate value and a pre-set stroke value and outputting a difference value according to the comparison result, and a stroke controller 2 for controlling an operation (stroke) of the reciprocating compressor 6 by varying a voltage applied to the motor according to the difference value.
The operation of the apparatus for controlling the operation of the compressor will now be described.
First, the current detector 4 detects a current applied to the motor (not shown) of the reciprocating compressor 6 and outputs the detected current value to the stroke calculator 5. At this time, the voltage detector 3 detects a voltage applied to the motor and outputs the detected voltage value to the stroke calculator 5.
The stroke calculator 5 calculates a stroke estimate value (X) of the reciprocating compressor 6 by substituting detected current value, the detected voltage value and the parameter of the motor to equation (1) shown below, and applies the stroke estimate value (X) to the comparator 1.
                    X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    M                                    -                  Ri                  -                                      L                    ⁢                                          i                      _                                                                      )                            ⁢                              ⅆ                t                                                                        (        1        )            wherein ‘R’ is a motor resistance value of the reciprocating compressor, ‘L’ is a motor inductance value, ‘α’ is a motor constant, VM is the value of the voltage applied to the motor, ‘i’ is the value of the current applied to the motor, and ī is a time variation rate of the current applied to the motor, namely, a differential value (di/dt) of ‘i’.
Thereafter, the comparator 1 compares the stroke estimate value and the pre-set stroke reference value and applies a difference value according to the comparison result to the stroke controller 2.
The stroke controller controls the stroke of the reciprocating compressor 6 by varying the voltage applied to the motor of the reciprocating compressor 6 based on the difference value.
FIG. 2 is a flow chart of a method for controlling the operation of the reciprocating compressor in accordance with the conventional art.
First, the stroke calculator 5 calculates a stroke estimate value of the reciprocating compressor 6 based on the detected current value, the detected voltage value and the parameter of the motor, and applies the calculated stroke estimate value to the comparator 1 (step S1).
The comparator 1 compares the stroke estimate value with the pre-set stroke reference value (step S2) and outputs a difference value according to the comparison result to the stroke controller 2.
If the stroke estimate value is smaller than the pre-set stroke reference value, the stroke controller 2 increases a voltage applied to the motor of the reciprocating compressor (step S3), whereas if the stroke estimate value is larger than the pre-set stroke reference value, the stroke controller 2 reduces the voltage applied to the motor of the reciprocating compressor (step S4).
However, with the conventional apparatus for controlling the operation of the reciprocating compressor, the stroke estimate value cannot be precisely calculated due to the parameter of the motor of the reciprocating compressor and a mechanical error of the reciprocating compressor, failing to precisely control the operation (stroke) of the reciprocating compressor 6.
As stated above, the apparatus and method for controlling the operation of the reciprocating compressor have such a problem that since the stroke estimate value cannot be precisely calculated due to the parameter of the motor of the reciprocating compressor and the mechanical error of the reciprocating compressor, the operation (stroke) of the reciprocating compressor cannot be precisely controlled.
U.S. Pat. No. 6,779,982 issued on Aug. 24, 2004 and U.S. Pat. No. 6,746,211 issued on Jun. 8, 2004 also disclose a conventional apparatus for controlling an operation of a reciprocating compressor.